Host cyclodextrins

Fig. 4.3 Schematic representation of the association-dissolation of the host (cyclodextrin) and guest (p-xylene). The formed guest/host inclusion complex can be isolated as a microcrystalline powder. (From ref. [13])...

In conclusion, it has found, when inherently immiscible polymers are simultaneously included as guests in the narrow channels of their common inclusion compounds (ICs) formed with host cyclodextrins (CDs) and then these polymer-l/polymer-2-CD-IC crystals are washed with hot water to remove the host CD lattice... 

Cyclodextrin - A Naturally Occurring Cyclic Host Cyclodextrins are cyclic hosts made from oligosaccharides. They provide a hydrophobic microenvironment in an aqueous phase. 

K. Hatton, K. Takahashi, M. Uematsu, N. Sakai, Multiple interactions between host cyclodextrin and guest compound assisting asymmetrically selective reduction with NaBH4 in aqueous media, Chem. Lett., 1990, 19, 1463-1466 K. Hattori, K. Takahashi, N. Sakai, Enantioface differentiating reduction of keto-acid in the presence of 6-deoxy-6-amino-j3-cyclodextrin with NaBHi in aqueous media. Bull. Chem. Soc. Jpn., 1992,65,2690-2696 K. Hattori, K. Takahashi, Asymmetric reduction of prochiral inclusion complex in aqueous media, Supramol. Chem., 1993, 2, 209-213. 

CB[n] are arguably the best of the families of molecular hosts (cyclodextrins, caUxarenes, cavitands...) for utilization as nanoreactors, due to their favorable properties. They contain rigid (for n < 8), spherical-shaped cavities, with... 

Both compounds exhibited three oxidation states. Cyclic voltammetry, in the presence of host / -cyclodextrin revealed that the Fc" "-Co form is not bound to this ligand, the Fc-Co oxidation state forming a stable complex by inclusion of the ferrocene site, while the fully reduced form Fc-Co presenting two binding sites for the CD host A large series of heterobimetallic metallocenes in which a zirconocene moiety was associated with another metallocene (M = Rh, Mn, Ru, Fe, Co, Zr, Hf) in the same molecule were synthesized in order to check their ability to polymerize ethylene. The Zr-Co member 365 of this series was shown to be among the most active catalysts, and it also provided the most uniform polymers (Figure 69). ... 

Crystalline packing of host cyclodextrins in solid cyclodextrin-inclusion compounds... 

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

P-Cyclodextrin is assumed to form host-guest complexes with diazonium ions (Fukunishi et al., 1982, 1985), but if so, complexation increases the extent of thermal dediazoniation, i. e., it has the contrary effect to that usually seen. 

A different non-classical approach to the resolution of sulphoxides was reported by Mikolajczyk and Drabowicz269-281. It is based on the fact that sulphinyl compounds very easily form inclusion complexes with /1-cyclodextrin. Since /1-cyclodextrin as the host molecule is chiral, its inclusion complexes with racemic guest substances used in an excess are mixtures of diastereoisomers that should be formed in unequal amounts. In this way a series of alkyl phenyl, alkyl p-tolyl and alkyl benzyl sulphoxides has been resolved. However, the optical purities of the partially resolved sulphoxides do not exceed 22% after... 

The kinetic effects of water and of cyclodextrins on Diels-Alder reactions. Host-guest chemistry, part 18 [65c]... 

The cyclodextrins also form channel-type complexes, in which the host... 

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

Dendritic hosts can be used in aqueous solution to encapsulate water-soluble fluorescent probes. Changes in the photophysical properties of these encapsulated probes are useful to understand the properties of the microenvironment created by the dendritic interior. For example, adamantyl-terminated poly(pro-pylene amine) dendrimers from the first to the fifth generation (36 represents the third generation) can be dissolved in water at pH<7 in the presence of -cyclodextrin because of encapsulation of the hydrophobic adamantyl residue inside the /1-cyclodextrin cavity and the presence of protonated tertiary amine units inside the dendrimer [72]. Under these experimental conditions, 8-anifi-... 

---